Dephosphorylation of Ser-137 in DARPP-32 by protein phosphatases 2A and 2C: different roles in vitro and in striatonigral neurons.
DARPP-32 (dopamine- and cAMP-regulated phosphoprotein, Mr=32000) is highly expressed in striatonigral neurons in which its phosphorylation is regulated by several neurotransmitters including dopamine and glutamate. DARPP-32 becomes a potent inhibitor of protein phosphatase 1 when it is phosphorylated on Thr-34 by cAMP- or cGMP-dependent protein kinases. DARPP-32 is also phosphorylated on Ser-137 by protein kinase CK1 (CK1), in vitro and in vivo. This phosphorylation has an important regulatory role since it inhibits the dephosphorylation of Thr-34 by calcineurin in vitro and in striatonigral neurons. Here, we show that DARPP-32 phosphorylated by CK1 is a substrate in vitro for protein phosphatases 2A and 2C, but not protein phosphatase 1 or calcineurin. However, in substantia nigra slices, dephosphorylation of Ser-137 was markedly sensitive to decreased temperature, and not detectably affected by the presence of okadaic acid under conditions in which dephosphorylation of Thr-34 by protein phosphatase 2A was inhibited. These results suggest that, in neurons, phospho-Ser-137-DARPP-32 is dephosphorylated by protein phosphatase 2C, but not 2A. Thus, DARPP-32 appears to be a component of a regulatory cascade of phosphatases in which dephosphorylation of Ser-136 by protein phosphatase 2C facilitates dephosphorylation of Thr-34 by calcineurin, removing the cyclic nucleotide-induced inhibition of protein phosphatase 1.
Desdouits
F
F
INSERM U114, Chaire de Neuropharmacologie, Collège de France, Paris, France.
Siciliano
J C
JC
Nairn
A C
AC
Greengard
P
P
Girault
J A
JA
D000595:Amino Acid Sequence; D000818:Animals; D047388:Casein Kinases; D002417:Cattle; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism; D051937:Dopamine and cAMP-Regulated Phosphoprotein 32; D066298:In Vitro Techniques; D009419:Nerve Tissue Proteins / Q000378:metabolism*; D009474:Neurons / Q000201:enzymology; D010749:Phosphoprotein Phosphatases / Q000378:metabolism*; D010750:Phosphoproteins / Q000378:metabolism*; D010766:Phosphorylation; D011494:Protein Kinases / Q000378:metabolism; D054645:Protein Phosphatase 1; D054648:Protein Phosphatase 2; D051381:Rats; D013378:Substantia Nigra / Q000201:enzymology*; D013696:Temperature
D051937:Dopamine and cAMP-Regulated Phosphoprotein 32; D009419:Nerve Tissue Proteins; D010750:Phosphoproteins; D011494:Protein Kinases; D047388:Casein Kinases; D017868:Cyclic AMP-Dependent Protein Kinases; D010749:Phosphoprotein Phosphatases; D054645:Protein Phosphatase 1; D054648:Protein Phosphatase 2